Basic information on infectivity and lethality of the gonococcus following inoculation into the yolk sac or intravenously has been obtained. These data will be used to develop models for neutralization tests and passive immunization of the chick embryo against infection, death, or toxic death. Sera in our collection will be used in these immunologic procedures. In addition, antisera will be produced in experimental animals inoculated with different fractions of virulent and avirulent gonococci, including pili, cell wall, cell membrane, and cytoplasm, and these antisera will be used in the procedures mentioned above. A variety of strains of Neisseria gonorrhoeae, of all colonial types, will be standardized by the yolk sac and intravenous routes and be used in the immunologic procedures. An attempt will be made to obtain gonococcal endotoxin by several methods and to assess its effects on the embryo. Studies are now being initiated to define parameters of gonococcal infection following inoculation on the dropped chorioallantoic membrane, and these will form the basis for neutralization and passive immune tests. In addition, the extent and manner of invasion by virulent (T-1 and T-2) gonococci will be assessed by both culture and electron microscopic analysis of various embryonic tissues following infection via several routes with standardized doses.